1. Technical Field
The present invention relates to a heat exchanger which is provided with tubes for flowing a medium and exchanges heat of the medium with heat conducted to the tubes.
2. Description of the Related Art
Generally, a heat exchanger such as a condenser, an evaporator, a radiator, a heater core or the like mounted on automobiles is provided with tubes for flowing a medium, fins fitted to the tubes and tanks which are connected to the tube ends and configured to perform the heat exchange of the medium with heat conducted to the tubes and the fins.
And, this type of heat exchanger is produced by assembling the tubes, fins and tanks which are made of aluminum or an aluminum alloy and heating the assembly in a furnace to be brazed into one body. A brazing material and flux necessary for the brazing are applied in advance to necessary portions of the respective members before heating.
As the tubes for the heat exchanger, those produced by shaping a plate-shaped material are known. And, these tubes are provided with beads which are shaped by bending a material, and the beads serve to improve a heat-exchange property and a pressure resistance of the tubes.
Besides, this heat exchanger has a sacrifice layer disposed on the outer surfaces of the tubes, so that the corrosion resistance of the tubes can be improved.
For example, the sacrifice layer which is formed of an Al—Zn based alloy is disposed on the core material of the tubes made of an Al—Mn based alloy, and electric potential of the tube core material becomes high with respect to the sacrifice layer. As a result, the corrosion resistance of the tubes is improved by a sacrificial anode effect.
When the tubes made of the plate-shaped material as described above are provided with beads, recessed portions are formed on the outer surfaces depending on the beads.
These recessed portions on the outer surfaces of the tubes make it difficult to connect the tubes and the tanks and the recessed portions readily gather dust and water, thus,they become a cause of advancing the corrosion of the tubes.
Especially, as described in Japanese Patent Laid-Open Publication No. HEI 4-20791, there are tubes in which the mutually opposed surfaces of the material at the beads are put together to eliminate the recessed portions of the outer surfaces. But, in practice, it is very hard to completely eliminate the recessed portions, and these tubes mostly have some recessed portions remaining on the outer surfaces.
When a brazing material is clad to the surface of the material which becomes the outer surface of the tube, the brazing material melted by heating accumulates in the recessed portions, so that the recessed portions can be filled with the brazing material. But, when the brazing material for filling the recessed portions is separately disposed on the tubes, there is a disadvantages that the production cost becomes very high.
Accordingly, in view of the above problem, it is an object of the present invention to provide a heat exchanger which can efficiently secure the corrosion resistance of the tubes and can be produced at a low cost.